Satellite quartet set to send weather reports from space when sunflares

Space physicist James Burch says he and his colleagues "eagerly anticipate the arrival of severe solar weather" as the sun enters the peak of its 11-year sunspot cycle. They've been through it before.

But this time new satellites will give them an unprecedented overview of what happens when solar outbursts rattle Earth's magnetic field. They urgently need this perspective to get a better grip on the rampaging particles and swirling electric currents that result. The potential these have to impair satellites and disrupt communications and power lines on Earth is well recognized.

There's new concern for airline passenger radiation safety should energetic particles penetrate to airline heights during the worst magnetic storms. This spring, the European Union required airlines to implement radiation training and dose-assessment procedures. The Federal Aviation Agency in the United States is considering whether or not to issue its own requirements. Some critics, such as In-Flight Radiation Protection Services in New York City, already recommend grounding airliners during rare, but dangerous, magnetic superstorms. The fact that such storms may one day delay your flight underscores the need for better space weather forecasting based on more thorough scientific understanding than Dr. Burch and other space physicists now have.

Scientists trying to trace sun-induced magnetic storms have been like meteorologists before the days of weather satellites. The best they could do was sketch overall patterns from scattered observations. Thomas Moore at NASA's Goddard Space flight Center in Greenbelt, Md., says it was like trying to understand thunderstorms "by driving around with a rain gauge out the window." No longer.

Burch, vice president of the Southwest Research Center in San Antonio, and Dr. Moore are on the scientific team for a satellite called IMAGE, launched March 25. Like a weather satellite viewing an entire hurricane, it gives space-storm trackers the big picture. It turns formerly invisible swirls of electric currents and particle flows into colorful images that scientists can knit into action movies.

Meanwhile, the European Space Agency (ESA) and several international partners, including NASA, are preparing to give the space-storm watchers 3-D vision. On July 16, a French-Russian Soyuz-Fregat rocket orbited the first pair of a spacecraft quartet called Cluster II. Launch of the second pair is scheduled for Aug. 9 from the Baikonur cosmodrome in Kazakhstan. They replace the original Cluster quartet lost on launch four years ago.

All four spacecraft have an identical suite of 11 instruments. ESA has named the craft Rumba, Salsa, Samba, and Tango to reflect "the way the four satellites will dance in formation," says ESA science director Roger-Maurice Bonnet.

Positioned at the corners of a triangular pyramid, they will provide what NASA calls "the unprecedented detail ... [needed] to assemble the first thorough three-dimensional maps of the environment that surrounds and protects our planet."

Earth is immersed in an interplanetary space dominated by the solar wind flowing outward from the sun. It is a wind of electrically charged particles - called plasma - and the magnetic fields they carry with them. Earth's own magnetic field deflects that outflow. It forms a protected region where Earth's magnetism dominates, controlling its own plasma flows. This is where the Van Allen radiation belts lie.

This normally placid scene can turn violent when the sun acts up. The sun, especially during its present active phase, can erupt in giant flares that bathe interplanetary space in relatively intense radiation. Sometimes the sun tears off part of its outer atmosphere and hurls billions of tons of plasma at Earth in what scientists call a coronal mass ejection. Like a scene from a space war movie, this solar "energy weapon" assaults Earth's magnetic field at speeds up to 4.5 million miles an hour. It buckles the shield and may force it below the height of the highest satellites. It penetrates weak spots, letting its plasma flow into the magnetosphere.

The result is glowing auroras and a swirl of electric currents that, in turn, induce disruptive currents in power lines and communications cables. Currents induced in oil pipelines speed corrosion. Meanwhile, satellites pick up electric charge, causing electric discharges and generating spurious command signals. Moreover, the storm can change the density of the thin residual atmosphere, where many satellites travel and alter their orbits.

With IMAGE and Cluster II, scientists will finally be able to monitor this show in its entirety. These new satellites join several other sun-watching and magnetosphere sampling spacecraft as part of the ongoing International Solar-Terrestrial Physics program.